(1) Field of the Invention
The present invention relates to a film having a gas barrier property, effective for prevention of the deterioration of organic EL device caused by oxygen and moisture, as well as to an organic EL device using such a film.
(2) Related Art Statement
Electroluminescent (hereinafter abbreviated as EL) devices are a light-emitting device utilizing the light emission of a solid fluorescent substance or electroluminescence.
Currently, inorganic EL devices using an inorganic material as a light-emitting substance are put to practical use in, for example, the backlight or flat display of liquid crystal display.
For organic EL devices, active development and research works are under way based on a prospect that such devices can be produced by a simple process at a low cost. Organic solids which are used as the light-emitting layer, hole transport layer, etc. of organic EL device, are generally weak to moisture and oxygen and incur formation of dark spots and reduction in luminance. In order to obtain a reliable organic EL device, the device need be produced in an encapsulated device form which can hinder the penetration of moisture and oxygen into the organic material and electrode material used therein.
Various proposals have been made for the method for encapsulating of organic EL device. These proposals include, for example, a method of encapsulating an organic EL device with a metal together with a hygroscopic material, and a method of providing a glass sheet outside the back electrode of an organic EL device and filling a silicone oil between the back electrode and the glass sheet for encapsulating. Also proposed is a method of encapsulating an organic EL device using an organic film of excellent gas-barrier property or a film having a vapor-deposited inorganic oxide layer.
As to the film used for encapsulating of an organic EL device, there are disclosed organic films made of a polychlorotrifluoroethylene (PCTFE) or the like; and transparent gas-barrier films obtained by forming, on a plastic substrate, an inorganic oxide film made of SiO2, Al2O3, MgO or the like, using physical vapor deposition (PVD) (e.g. vacuum vapor deposition, sputtering or ion plating) or chemical vapor deposition (CVD) (e.g. plasma chemical vapor deposition, thermal chemical vapor deposition or photochemical vapor deposition).
Organic polymers used for ordinary food packaging have an oxygen permeability of several tens to several hundreds cc/(m2xc2x7day) and a moisture permeability of several tens to several hundreds g/(m2xc2x7day). In contrast, organic polymers having a molecular structure having particularly a reinforced barrier property such as polychlorotrifluoroethylene (PCTFE) have an oxygen permeability of several cc/(m2xc2x7day) and a moisture permeability of several g/(m2xc2x7day).
Meanwhile, gas-barrier films obtained by forming, on a plastic substrate, an inorganic oxide film made of SiO2, Al2O3, MgO or the like, using PVD or CVD are dense and, for example, a vapor-deposited SiOx film of 5 xcexcm in thickness formed on a PET substrate of 30 xcexcm in thickness has an oxygen permeability of about 1 cc/(m2xc2x7day) and a moisture permeability of about 1 g/(m2xc2x7day). It is disclosed in JP-A-11-80934 that an aluminum oxide/aluminum hydroxide composite film, which is obtained by a simple process of vapor-depositing Al2O3 on a plastic substrate, subjecting the surface of the resulting Al2O3 film to a plasma treatment with oxygen gas, and then introducing hydroxyl group into the Al2O3 film after plasma treatment, has an oxygen permeability of 1.2 cc/(m2xc2x7day) and a moisture permeability of 2.0 g/(m2xc2x7day). It is also disclosed in JP-A-11-332979 that a film, which is obtained by subjecting the surface of a PET substrate to a plasma treatment with oxygen gas and then forming thereon a vapor-deposited inorganic oxide film, has an oxygen permeability of 0.9 cc/(m2xc2x7day) and a moisture permeability of 0.8 g/(m2xc2x7day).
The encapsulating material used in organic EL devices is required to have transparency and also a gas-barrier property which is higher than those possessed by conventional food packaging materials. Any of the above-mentioned gas-barrier organic films and vapor-deposited inorganic material films, however, has no sufficient gas-barrier property to encapsulate organic EL devices. In order to allow known gas-barrier organic films to have a gas-barrier property sufficient for encapsulating organic EL devices, it is necessary to allow them to have a larger thickness of about 10 cm. Vapor-deposited inorganic material films show as well a decrease in gas permeability by allowing them to have a larger thickness; however, when the thickness is 100 nm or more, the gas permeability reaches the minimum value and shows no further decrease. Thus, it is difficult to achieve a gas-barrier property sufficient for encapsulating organic EL devices by increasing the thickness of vapor-deposited inorganic material films. Therefore, it is not practical to use a conventional gas-barrier organic polymer film or a conventional vapor-deposited inorganic material film in an organic EL device, by increasing the thickness of the film.
Other methods for encapsulating an organic EL device were also proposed, but they have problems in obtaining a light and thin organic EL device.
The objects of the present invention are to provide a film for organic EL device, having a gas-barrier property sufficient for protection of organic EL device, and an organic EL device structure using such a film.
The present inventors made an extensive study in order to alleviate the above-mentioned problems. As a result, the present inventors found out that organic inorganic hybrid materials having fluorine group and siloxane group, for example, organic inorganic hybrid materials having a basic skeleton of polychlorofluoroethylene and containing an organic skeletal moiety and an inorganic skeletal moiety, have an excellent gas-barrier property. The present inventors further found out that a multi-layered sheet obtained by forming, on a plastic substrate, a film made of the above-mentioned organic inorganic hybrid material and a vapor-deposited inorganic material film has a higher gas-barrier property than only the organic inorganic hybrid material and that a laminate of a plurality of such multi-layered sheets has an even higher gas-barrier property. The above findings have led to the completion of the present invention.
The essence of the present invention lies in a film for use in organic EL device, made of an organic inorganic hybrid material whose molecules have an organic skeletal moiety and an inorganic skeletal moiety and contain fluorine group and siloxane group.